The present invention relates to electronic keys, and to integrated circuits having secure memory therein.
Electronic Keys
An electronic key is a circuit which performs the function of a key, using stored information instead of shaped metal. An electronic key may have to withstand harsh environments (such as users' pockets), and is therefore packaged to provide a high degree of physical robustness. Similarly, it is desirable to maximize the immunity of electronic keys to electrostatic discharge..sup.1 Electronic keys, and related circuits, have found use in a wide variety of applications. FNT .sup.1 See U.S. application Ser. No. 345,144, filed Apr. 28, 1989, entitled "Integrated Circuit Protected Against Negative Transients" abandoned, which is hereby incorporated by reference.
However, electronic keys present some unusual difficulties in design. There is always some risk that an intruder may obtain a key and attempt to "crack" it, to gain free access to the system which is supposed to be protected. Thus, although perfect security may not be possible, the design must provide as much security as is economically possible.
Electronic keys are used primarily to provide access to secure electronic data upon receipt of a valid password and to prohibit such access if an invalid password is received. One such application is the use of an electronic key hardware module in conjunction with commercially available software. The electronic key module is attached to the computer operating the software in a manner to allow the software to access the electronic key, and the software is programmed with an algorithm to verify that the module is attached to the computer. Thus, while the software is easily copied, the electronic key hardware module is not; and the software cannot, therefore, be simultaneously used in several computers.
Although many demonstrations and uses of electronic keys have occurred (since at least the 1960s), electronic keys never became common until well into the 1980s.